More uncommon than the rise of the Communist Party (5)
I believe the answer is:
odder
'more uncommon' is the definition.
(I've seen this in another clue)
'rise of the communist party' is the wordplay.
'rise of' says the letters should be written in reverse (in a down clue, letters go up).
'the communist' becomes 'red' (red can informally mean communist).
'party' becomes 'do' (do is a kind of party).
'red'+'do'='reddo'
'reddo' written backwards gives 'ODDER'.
'than the' acts as a link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for odder that I've seen before include "more rum" , "More unusual" , "More strange or less even" , "More peculiar" , "Stranger" .)